1. Field of the Invention
The present invention relates to a dynamic bearing device. This dynamic bearing device are suitable as a bearing device for use in a spindle motor of an information apparatus, for example, a magnetic disc apparatus, such as an HDD, an optical disc apparatus, such as a CD-ROM, a CD-R/RW, or a DVD-ROM/RAM, or a magneto-optical disc apparatus, such as an MD or an MO, a polygon scanner motor for a laser beam printer (LBP), a color wheel for a projector, or a small motor for an electric apparatus, such as an axial flow fan.
2. Description of the Related Art
Apart from high rotational accuracy, an improvement in speed, a reduction in cost, a reduction in noise, a reduction in weight, etc. are required of the motors as mentioned above. One of the factors determining such requisite performances is the bearing supporting the spindle of the motor. Recently, as a bearing of this type, use of a dynamic bearing superior in the above requisite performances is being considered, or such a dynamic bearing has been actually put into practical use.
JP 2002-061641 A discloses an example of the dynamic bearing as mentioned above which is equipped with a radial bearing portion supporting a rotary member having a shaft portion and a flange portion in the radial direction in a non-contact manner and a thrust bearing portion supporting the rotary member in the thrust direction in a non-contact manner. In a dynamic bearing device of this type, dynamic pressure grooves as dynamic pressure generating means are provided in the inner peripheral surface of a bearing sleeve constituting the radial bearing portion or in the outer peripheral surface of the shaft portion. Further, dynamic pressure grooves are provided in both end surfaces of a flange portion constituting the thrust bearing portion, or in surfaces opposed thereto (e.g., the end surfaces of the bearing sleeve, and an end surface of the bottom portion of a housing).
The housing is usually equipped with a cylindrical side portion and a bottom portion provided at one end of the side portion. The bottom portion is fixed to the inner periphery at one end of the side portion as a bottom member separate from the side portion; alternatively, it is formed integrally with the side portion. This is mainly formed of metal. For less expensive formation thereof, JP 2003-314534 A discloses a dynamic bearing equipped with a housing formed of resin.
Further, for example, in a spindle motor for an apparatus for driving a recording disk, such as a hard disk, there is used a dynamic bearing device which is equipped with a radial bearing portion supporting a rotary member in the radial direction in a non-contact manner by a dynamic pressure action of a lubricant fluid generated in a radial bearing clearance between the rotary member and a bearing sleeve, and a thrust bearing portion supporting the rotary member in the thrust direction in a non-contact manner by a dynamic pressure action of the lubricant fluid generated in a thrust bearing clearance between a housing and the rotary member (see, for example, JP 2000-291648 A). Further, the apparatus for driving a recording disk, such as a hard disk, is used in a relatively wide temperature range, so that a lubricant fluid of low evaporation rate and low viscosity is suitable for a dynamic bearing device to be used in the spindle motor of such a recording disk driving apparatus. For example, an ester type lubricating oil is used (see, for example, JP 2003-172336 A).
High machining precision and high assembly precision are required of the components of a dynamic bearing device, including the housing, in order to secure a high rotation performance as required with the recent increasing improvement of information apparatuses. Further, as the information apparatuses undergo a reduction in size and weight, a reduction in size and weight of the dynamic bearing devices is also required. At the same time, the requirement for a reduction in the cost of a dynamic bearing device is becoming increasingly severe.
Further, an ester type lubricating oil used in a dynamic bearing device of this type contains an ester group and thus has high reactivity with other components. Thus, there is a fear of a product generated through the reaction of the resin material forming the housing with the lubricating oil causing denaturing degeneration in the lubricating oil or a deterioration in the cleanliness of the bearing device.
Further, the resin housing is formed usually through injection molding of a resin material, which generates a gas (out gas) in a high temperature atmosphere. In particular, in the case of a bearing device to be used in an apparatus for driving a recording disk, such as a hard disk, the out gas generated in the high temperature atmosphere causes a deterioration in the cleanliness of the bearing device or the recording disk driving apparatus, such as contamination of the surface of the hard disk.